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Tue, 26 Nov 2024 09:32:33 -0800 (PST) Message-ID: Subject: Re: [PATCH dwarves v2 1/1] btf_encoder: handle .BTF_ids section endianness From: Eduard Zingerman To: Arnaldo Carvalho de Melo Cc: Jiri Olsa , dwarves@vger.kernel.org, arnaldo.melo@gmail.com, bpf@vger.kernel.org, kernel-team@fb.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, yonghong.song@linux.dev, Alan Maguire , Daniel Xu , Kumar Kartikeya Dwivedi , Vadim Fedorenko , Vadim Fedorenko Date: Tue, 26 Nov 2024 09:32:28 -0800 In-Reply-To: References: <20241122214431.292196-1-eddyz87@gmail.com> <20241122214431.292196-2-eddyz87@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.1 (3.54.1-1.fc41) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2024-11-26 at 13:25 -0300, Arnaldo Carvalho de Melo wrote: [...] Hi Arnaldo, > I think I saw instructions in one of the messages in this thread to get > hold of a vmlinux for s390 and test it. Right? Yes, in cover letter. Full vmlinux is not needed, a vmlinux binary for s390 would be sufficient for testing. Repeating the recipe for convenience: To reproduce the bug: - follow the instructions in [0] to build an s390 vmlinux; - generate BTF requesting declaration tags for kfuncs: $ pahole --btf_features_strict=3Ddecl_tag_kfuncs,decl_tag \ --btf_encode_detached=3Dtest.btf vmlinux - observe that no kfuncs are generated: $ bpftool btf dump file test.btf format c | grep __ksym [0] https://docs.kernel.org/bpf/s390.html > One extra question: this solves the BTF encoder case, the loader already > supported loading BTF from a different endianness, right? Lemme > check. >=20 > cus__load_btf() > cu->little_endian =3D btf__endianness(btf) =3D=3D BTF_LITTLE_ENDIAN; >=20 > enum btf_endianness btf__endianness(const struct btf *btf) > { > if (is_host_big_endian()) > return btf->swapped_endian ? BTF_LITTLE_ENDIAN : BTF_BIG_= ENDIAN; > else > return btf->swapped_endian ? BTF_BIG_ENDIAN : BTF_LITTLE_= ENDIAN; > } I can switch to is_host_big_endian() instead of `BYTE_ORDER` macro if you think that's better. > So we have parts of BTF byte swapping happening in libbpf and with this > patch, parts of it done in pahole, have you tought about doing this in > libbpf instead? BTF id lists handling is currently not a part of libbpf. Thanks, Eduard